If you'll remember, I suggested unjustly making Walker a sacrificial lamb for our end-of-season collapse last year, as a Fergie-esque way to build a fear of failure in the side - it's because I saw him as the least irreplaceable of our first eleven. That still holds, I guess - he's come on in leaps and bounds and really become an outstanding, hard-working, committed member of the side, but a) there are still other RBs we can get to smooth over the (hopefully) long-term transition from him to KWP, b) Trippier's a very acceptable backup and could likely hold his own in that RWB slot full-time for a season or so if necessary, and c) there are currently more talented RBs out there than there are left-backs - much like there are more RCBs out there than there are LCBs. Thus, if we *had* to lose one of our dynamic duo, I'd rather lose Walker than Rose.
One thing's for sure, though - if Walker leaves, it's because Poch wants him gone, and not because he thinks he can swan in and out of the club with no issues. And, given that situation and his very long contract, I suspect the windfall we receive from his (possible) sale could be used to get a genuinely top-class player in an alternate position that would usually be outside our price range (50m mark, perhaps), or at least an RB of equivalent skill and potential.